sea foam algae with pale frothy tufts in the surge zone
- Size
- Height: 5–15 cm
- Lifespan
- 1–2 years
- Diet
- Photosynthetic - grows in sheltered bays, rock pools, and estuaries. Requires still water, good light, and high nutrient levels. Forms foam-like, bubbly fronds that are bright green.
- Habitat
- The sea foam algae grows in open coastal waters throughout New Zealand – from Northland down to Stewart Island, particularly in the spring and summer when the water warms and the nutrients are abundant. It is a creature of the bloom, the surge, the places where the sea turns to foam. It forms floating colonies of microscopic cells that create thick, white, frothy foam on the surface of the water. It looks harmless, like sea foam or whipped cream. But it is not always harmless.
- Range
- New Zealand - found throughout the North and South Islands in sheltered bays, rock pools, and estuaries. Most common in lowland coastal waters with high nutrient levels.
- Endemism
- Native
- Main Threats
- None significant - this species is common and widespread in nutrient-rich waters. Localised threats include coastal development and pollution. Classified as Not Threatened.
- Population
- Not Threatened, but it can cause problems when it blooms. Sea foam algae is naturally present in New Zealand waters, but it can form dense blooms under the right conditions – warm water, still weather, and high nutrient levels. These blooms can be large, covering hectares of sea surface. It is not rare. It is just very, very foamy.
- Conservation Status
- Not Threatened
The sea foam algae is the one that turns the sea to foam. You have seen it – a thick, white, frothy scum on the surface of the water, like someone poured detergent into the sea. The foam is made of millions of microscopic colonies, each one a sphere of cells embedded in a gel-like matrix. When the colonies break apart, they release the gel, which mixes with the water and the air to form foam.
What makes it special? The foam. The foam can be metres thick, drifting across the surface of the sea, washing up on beaches like a white blanket. It is soft and fluffy, like whipped cream or meringue. Children love to play in it. But it has a dark side.
The sea foam algae produces a chemical called dimethylsulfoniopropionate (DMSP), which breaks down into dimethyl sulfide (DMS) – the gas that gives the sea its distinctive, salty smell. DMS also plays a role in cloud formation, seeding the sky with particles that water vapour can condense around. The sea foam algae is not just a nuisance. It is a player in the global climate.
When the sea foam algae blooms, it can cause problems. The foam can be irritating to the skin and eyes. When the bloom dies and decays, it uses up oxygen in the water, creating dead zones. Some blooms produce toxins that can harm fish and other marine life. It looks harmless, but it is not always harmless.
Biologically, the sea foam algae is a haptophyte – a type of planktonic alga. It reproduces by cell division, forming colonies that can grow rapidly under ideal conditions.
The sea foam algae is a reminder that the sea is not just water and waves. It is alive with microscopic creatures, creatures that can turn the sea to foam, that can change the climate, that can be beautiful and dangerous at the same time.